Definitions
Nearby Words

# 61 (number)

61 (sixty-one) is the natural number following 60 and preceding 62.

## In mathematics

It is the 18th prime number. The previous is 59, with which it comprises a twin prime. Sixty-one is a cuban prime of the form $p = \left(x^3 - y^3\right) / \left(x - y\right), x = y + 1$.

Sixty-one might be the largest prime that divides the product of the next two primes plus 1. If there is a larger such prime, it would have to be greater than 179424673.

Sixty-one is the sum of two squares, 52 + 62, and it is also a centered square number, a centered hexagonal number and a centered decagonal number.

Since 8! + 1 is divisible by 61 but 61 is not one more than a multiple of 8, 61 is a Pillai prime. In the list of Fortunate numbers, 61 occurs thrice, since adding 61 to either the tenth, twelfth or seventeenth primorial gives a prime number (namely 6469693291, 7420738134871 and 1922760350154212639131).

It is also a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 6, 1, 7, 8, 15, 23, 38, 61...

## In science

The chemical element with the atomic number 61 (promethium), a lanthanide, is the element with the secondary lowest ordinal number, which does not possess any stable isotopes. The promethium preceding element with atomic number 60 (neodymium) and the promethium following element 62 (samarium) have all stable isotopes.

## In other fields

Sixty-one is:

• The number of the French department Orne
• The code for international direct dial phone calls to Australia
• Sixty-one thousand (61,000) darics of gold was apparently donated as freewill offerings for the building of a new Temple in Jerusalem when the Jewish exiles returned from their Babylonian captivity: As soon as they came to the house of the LORD in Jerusalem, some of the heads of the families made freewill offerings for the house of God, to erect it on its site. According to their resources they gave to the building fund sixty-one thousand darics of gold, five thousand minas of silver, and one hundred priestly robes. (Ezra chapter 2, verses 68 and 69 (New Revised Standard Version of the Bible); Nehemiah chapter 7, verses 70 to 72 has a slightly different record, though that record may be partly intended to reflect donations to more than simply Temple building construction, or Nehemiah's book may simply be a varying account (Nehemiah lists the governor as donating 1,000 darics of gold, fifty basins, and 530 priestly robes along with the ancestral heads of families donating 20,000 darics of gold, 2200 minas of silver, and the rest of the people who also gave 20,000 darics of gold, 2000 minas of silver and 67 priestly robes.
• 61*, a 2001 baseball movie directed by Billy Crystal
• Sixty-one is a number often related to the Colonel's insane speech in Metal Gear Solid 2: Sons of Liberty
• The Highway 61 Blues Festival occurs in June in Leland, Massachusetts
• Part 61 is a law created by the FAA regarding medical exams. This law has often come under attack by AOPA.
• Highway 61 Revisited is a Bob Dylan album
• The P-61 is the Northrop designed fighter first designated as the XP-61. It first flew on May 26, 1942. It is also known as the Black Widow as it was the first fighter aircraft designed to be a night fighter
• Sixty 1 brand tobacco produced by Nationwide Tobacco
• At age 61, W.C. Fields starred in Never Give a Sucker an Even Break 1941
• There's a music sharing site for indie artists called thesixtyone.com
• At age 61, President Harry Truman decided to drop atom bomb in 1945
• At age 61, President Richard Nixon, resigned the presidency in 1974. He was succeed by Gerald Ford, also age 61
• 61A is the London address of Margot Wendice (Grace Kelly) and Tony Wendice(Ray Milland) in the movie "Dial M for Murder"
• 1 Liberty Place is Philadelphia's tallest building at 61 stories

## Historical years

61 A.D., 61 B.C., 1961, 2061, etc.

## References

• R. Crandall and C. Pomerance (2005). Prime Numbers: A Computational Perspective. Springer, NY, 2005, p. 79.